Conventional part-time four-wheel drive vehicles are typically equipped with a drive train to transmit rotary power from the power train to a front pair of drive wheels and/or a rear pair of drive wheels. The front axle assembly is connected to a front driveshaft and the rear axle assembly is connected to the rear driveshaft. The gear teeth, splines or mechanical interfaces with the gear sets in the driveshaft mesh with the gear teeth, splines or mechanical interfaces of interfacing gear sets in the front and rear drive trains. There is a small amount of clearance between the gear teeth in the interfacing gears. Throughout this document, the phrase “teeth” refers to gear teeth, splines or mechanical interfaces in a gear set and the phrase “tooth” refers to a gear tooth, a spline or a mechanical interface in a drive train.
When the throttle level in the four-wheel drive vehicle changes or a transmission gear shift occurs, the torque on the driveshafts change. The torque change results in backlash at interfaces connecting different rotating components. The backlash occurs at the transfer case chain to sprocket interfaces, at the sprocket to driveshaft interfaces, at the driveshaft universal joints, at the driveshaft slip joints, and at the axle differential gear set to driveshaft interfaces. Specifically, the gear teeth in a gear on a first component impact the gear teeth in a gear on a second interfacing component when the angular velocity of the first component decreases or changes direction before the angular velocity of the second interfacing component has likewise changed.
The driver can experience the backlash as jolting vibration in the vehicle, which is typically called “clunk.” In many cases, the clunk is audible to the driver. The intensity of the clunk is related to the number of backlash events, the relative timing of backlash events in the vehicle, and the amount of backlash in the system.
In a four-wheel drive vehicle, the front driveshaft and rear driveshaft can experience differing amounts of backlash. The amount of angular rotation change of the front driveshaft before impact with the meshed gear teeth in the interfacing front driveshaft components can be more or less than the amount of angular rotation change of the rear driveshaft before impact with the meshed gear teeth in the interfacing rear driveshaft components. Any difference in the amount of rotation change between the front driveshaft components and the rear driveshaft components extends the duration of the backlash-induced clunk experienced by a driver and passengers in the vehicle.
It is desirable to overcome these and other disadvantages when the angular velocity changes for the components of a drive train. It is further desirable to reduce the backlash in the drive train of a four-wheel drive vehicle.